DOC: added examples to DataFrame.var #44162

[ruankie]

• closes DOC: var and std missing examples #44162 by adding two examples to docstring of DataFrame.var
• tests added / passed
• All linting tests passed (pre-commit)

Screenshot of locally built documentation:

[MarcoGorelli]

Nice, thanks @ruankie

Looks like there's some old commits here, but they'll get squashed together when merging anyway so it's fine

[ruankie]

Thanks @MarcoGorelli for the motivation via cat images.
Apologies for the old commits. Next time I'll create a new branch from scratch.

[ruankie]

It seems like there is a check that keeps failing CI > Checks (pull_request) > Typing validation. I do not understand the error report so I'm not sure what is going wrong. Please see the details of the error report below and advise:

Run ci/code_checks.sh typing
mypy --version
mypy 0.910
Performing static analysis using mypy
pandas/core/frame.py:997: error: Incompatible return value type (got "Optional[str]", expected "str")  [return-value]
Found 1 error in 1 file (checked 1318 source files)
Performing static analysis using mypy DONE
Performing static analysis using pyright
No configuration file found.
pyproject.toml file found at /home/runner/work/pandas/pandas.
Loading pyproject.toml file at /home/runner/work/pandas/pandas/pyproject.toml
Assuming Python platform Linux
Searching for source files
Found 311 source files
0 errors, 0 warnings, 0 infos 
Completed in 48.921sec
Performing static analysis using pyright DONE
Error: Process completed with exit code 1.

[MarcoGorelli]

It seems like there is a check that keeps failing CI > Checks (pull_request) > Typing validation. I do not understand the error report so I'm not sure what is going wrong. Please see the details of the error report below and advise:

Run ci/code_checks.sh typing
mypy --version
mypy 0.910
Performing static analysis using mypy
pandas/core/frame.py:997: error: Incompatible return value type (got "Optional[str]", expected "str")  [return-value]
Found 1 error in 1 file (checked 1318 source files)
Performing static analysis using mypy DONE
Performing static analysis using pyright
No configuration file found.
pyproject.toml file found at /home/runner/work/pandas/pandas.
Loading pyproject.toml file at /home/runner/work/pandas/pandas/pyproject.toml
Assuming Python platform Linux
Searching for source files
Found 311 source files
0 errors, 0 warnings, 0 infos 
Completed in 48.921sec
Performing static analysis using pyright DONE
Error: Process completed with exit code 1.

It's unrelated, and fixed on master, don't worry about it

[ruankie]

It's unrelated, and fixed on master, don't worry about it

Ok great. Is there anything else I can do regarding this PR before it can be merged?

[MarcoGorelli]

Looks good to me, I'll just leave it open a bit in case others have comments

[ruankie]

Good idea, thanks @MarcoGorelli

[ruankie]

Thanks, @mroeschke
Just made the changes you recommended.

[mroeschke]

Thanks @ruankie